Cystic fibrosis is the most common lethal hereditary disease among Caucasians and it is characterized by a biochemical abnormality in CFTR (cystic fibrosis transmembrane conductance regulator) channel. The most common clinical manifestation in cystic fibrosis is chronic lung infection that leads to progressive tissue destruction and elevated pulmonary morbidity and mortality. Lung tissue damage in cystic fibrosis has been related to an abnormally exacerbated immune response in cystic fibrosis cells. This exacerbation has been related to an exaggerated activation of the pro-inflammatory transcriptional factor NF-κB.
One molecule that is known to inhibit NF-κB activation is ceramide (N-acylsphingosine; Signorelli, et al. (2001) FASEB J. 15:2401-2414), a sphingolipid recognized as a second messenger in the molecular modulation of apoptosis. The sphingomyelin cycle, with the conversion of sphingomyelin to ceramide by sphingomyelinase (SMase), is a key signaling pathway in many cell systems (Hannun, et al. (1996) Science 274(5294):1855-9). Two main routes have been defined for the generation of ceramide including hydrolysis of sphingomyelin, an abundant sphingolipid species in cell membranes, by the action of SMases; and by de novo biosynthesis catalyzed by ceramide synthase (Levade and Jaffrezou (1999) Biochim. Biophys. Acta 1438:1-17). The hydrolytic pathway, however, is the major source for ceramide in cellular responses to extracellular signaling, i.e., tumor necrosis factor-alpha (TNF-α), lipopolysaccharides, gamma-interferon, and interleukins (Chan and Goldkorn (2000) Am. J. Respir. Cell Mol. Biol. 22:460-468).
Treatment of cells in culture with TNF-α has emerged as one of the best-characterized models of cytokine-induction and of ceramide function. TNF-α induces activation of SMase in these cells and this activation is a consequence of the drop of glutathione that follows the activation of the death receptor and caspase 8 (Liu, et al. (1998) J. Biol. Chem. 273:11313-11320; Luberto, et al. (2000) J. Biol. Chem. 275:14760-14766). Conversely, extracellular supplementation of glutathione or N-acetylcysteine, a known precursor of glutathione, inhibit ceramide generation induced via oxidative stress caused by agents such as TNF-α, interleukin-1-β, hypoxia, and daunorubicin (Beaver and Waring (1995) Eur. J. Cell Biol. 68:47-54; Liu, et al. (1998) supra; Singh, et al. (1998) J. Biol. Chem. 273:20354-20362; Lavrentiadou, et al. (2001) Am. J. Respir. Cell Mol. Biol. 25:676-684). Glutathione inhibits the activation of the neutral, magnesium-dependent SMase and inhibits ceramide generation induced by TNF-α in human mammary carcinoma cells (Liu, et al. (1998) supra). In addition, it has been shown that low glutathione levels in lung cells were required for ceramide production, whereas high glutathione levels inhibit the generation of ceramide (Lavrentiadou, et al. (2001) supra).
Fenretinide, i.e., N-(4-hydroxyphenyl)retinamide (4-HPR) a synthetic derivative of retinoic acid, has been shown to increase endothelial ceramide by de novo, non-sphingomyelinase-mediated synthesis (Erdreich-Epstein, et al. (2002) J. Biol. Chem. 277:49531-49537) resulting in caspase-dependent endothelial apoptosis of human brain microvascular endothelial cells. Accordingly, fenretinide is suggested for use in cancer prevention.
U.S. Pat. No. 6,368,831 discloses a method of treating a hyperproliferative disorder (including tumors, cancers, and neoplastic tissue, along with pre-malignant and non-neoplastic or non-malignant hyperproliferative disorders) in a subject in need of such treatment using a ceramide-generating retinoid such as fenretinide and ceramide degradation inhibitor. This patent teaches that premalignant and non-neoplastic or non-malignant hyperproliferative disorders include but are not limited to myelodysplastic disorders; cervical carcinoma-in-situ; familial intestinal polyposes such as Gardner syndrome; oral leukoplakias; histiocytoses; keloids; hemangiomas; hyperproliferative arterial stenosis, inflammatory arthritis; hyperkeratoses and papulosquamous eruptions including arthritis.
U.S. Pat. No. 6,610,835 teaches that biologically important sphingolipids can be administered as prodrugs (e.g., ceramide β-glucuronide) which increase the level of active compound that is delivered to the active site of interest. The prodrug is cleaved by an appropriate enzyme in vivo to release a parent sphingolipid moiety for desired therapy. This reference teaches that the disclosed prodrugs are useful in the treatment of disorders of the lower intestinal tract, including but not limited to colon cancer, intestinal polyps, intestinal tumors, inflammatory bowel diseases including ulcerative colitis and Crohn's disease, necrotizing enterocolitis, ileocecitis, and other inflammations of the lower bowel.